The invention relates to a folding circuit for an analog-to digital converter for converting a monotonously increasing input signal to a certain value thereof into a monotonously increasing or decreasing output signal and, above that value, into a monotonously decreasing or increasing output signal, the folding circuit comprising a first and a second transistor to which the input signal is applied in operation and whose emitters are fed by a first and a second d.c. current source, respectively, and from whose collectors the output signal is obtained by means of a difference-producing circuit.
IEEE Transactions on Nuclear Science, Vol. NS 22, February 1975, pages 446-451 describes an analog-to-digital converter of the type defined above which comprises a folding circuit wherein the input signal is applied to the bases of a first and a second transistor. Each emitter of the first and the second transistor is connected to an emitter of one of two other transistors the bases of which being connected to a somewhat different reference voltage. Such a folding circuit has an input signal-output signal characteristic which greatly deviates from the desired triangular shape. A slight improvement thereof is possible by the use of logarithmic load resistors.